Abstract:
Halide perovskites are well known for their intrinsically ultralow lattice thermal conductivity, which originates from strong lattice anharmonicity arising from weak metal–halide bonding, soft polyhedral dynamics, and stereochemically active lone-pair electrons. Despite extensive studies based on the conventional phonon-gas model, our recent investigations suggest that propagating phonons alone may not fully account for heat transport in these highly anharmonic crystals, implying an additional contribution from diffuson-mediated thermal transport. To elucidate the respective roles of phonons and diffusons, the lattice thermal conductivity and corresponding phonon spectra of 0D–3D halide perovskite single crystals were systematically investigated over a wide temperature range. We demonstrate that a dual phonon–diffuson transport framework provides a more complete description of lattice thermal transport than the conventional phonon-gas model. Quantitative analysis of the relative contributions of propagating phonons and diffusons across different structural dimensionalities further indicates that the connectivity of metal–halide octahedra/tetrahedra plays a key role in governing vibrational coupling, mode localization, and the relative contributions of phonon- and diffuson-mediated heat transport.
Keywords – Halide perovskites; Phonon transport; Diffusons; Lattice anharmonicity; Inelastic neutron scattering.